Chapter 6 - Rotating Cylinders, Annuli, and Spheres

Abstract

This chapter describes the principal flow phenomena, and develops and presents methods to determine parameters such as the drag associated with a rotating cylinder and local flow velocities. The flow phenomenon in rotating cylinder applications depends on the orientation of the cylinder to the flow and the axis of rotation. Correlations are available to determine the drag associated with rotating shaft applications. For an annulus where the inner or outer cylinder may be rotating, consideration can be given to the stability of the flow in order to identify whether vortices are likely to form. Under certain conditions of inner cylinder rotation or combined inner and outer cylinder rotation, toroidal vortices can form in an annulus known as Taylor vortices, with alternate vortices rotating in opposite directions. Rotation of a cylinder or sphere in a cross-flow causes a deflection of the fluid stream and as a result a force due to reaction on the cylinder or sphere concerned. This phenomenon can be exploited to provide a propulsive mechanism for ships and boats using winds to provide the cross-flow; in sports, the variability in lift and drag with spin rate is exploited to control the trajectory and bounce of a shot and in some cases to provide ball or projectile flight paths that are more difficult to predict.